The field of the invention is in digital to analog converters, and more particularly in that of providing an analog tuning voltage with multiplexing.
Many modern communication devices such as radio receivers use an electronic frequency synthesizer having a digitally controlled analog voltage in a VCO (voltage controlled oscillator) circuit for tuning. The need for more stable, accurate, and less space consuming circuits has been well recognized.
The best known prior art is that contained in U.S. Pat. No. 3,624,530 to patentee Zwirn; U.S. Pat. No. 3,904,977 to patentee Barsotti; and U.S. Pat. No. 4,015,192 to patentee Koyanagi; and the article "CMOS Analog switches can precisely control a op-amp's gain", by Gordon L. Wong appearing in Electronic Design 10, May 10, 1976.